In all works of science fiction, there are ten hidden assumptions regarding alien races. None of these assumptions is a necessity. None of them makes immanent or inevitable sense. Yet, when we read a sci-fi novel or watch a sci-fi movie we tend to accept all of them as inescapable. They amount to a frame of reference and to a language without which we seem to be unable to relate to all manner of exobiology. We evidently believe that life on Earth is a representative sample and that we can extrapolate its properties and mechanisms of action wide and far across the Universe. The principles of symmetry, isotropy, and homogeneity apply to the physical cosmos: Hydrogen behaves identically in our local galactic neighbourhood as it does in the furthest reaches of the Cosmos. Why shouldnât life be the same?